Thailand faced mounting calls on Thursday to stop pushing migrants back out to sea amid fears an exodus of Rohingya Muslims from Burma could spark a new wave of boatpeople.

Fighting in Burma’s northern Arakan State has forced about half a million Rohingya to seek refuge in neighbouring Bangladesh since August, prompting concerns they could be targeted by people smugglers and human traffickers.

Rohingya Muslims, who are denied citizenship in Buddhist-majority Burma, have been fleeing strife for decades.

Neighbouring Thailand was a popular transit route by boat and land until a 2015 Thai police crackdown led to ships full of migrants being abandoned at sea.

“Thailand urgently needs to set a regional example by adopting humane refugee policies,” said Audrey Gaughran from Amnesty International as the group released a report accusing Thai authorities of failing to protect refugees.

“Instead of callously repelling people fleeing unimaginable horrors, the Thai government should ensure safe passage for those seeking international protection in Thailand,” said the global issues director.

Campaigners say the Rohingya are likely to start travelling after the monsoon in late November when the water is calmer.

Thai Prime Minister Prayuth Chan-ocha said last month his government is “preparing to receive” people fleeing Burma and send them back “when they are ready.”

But the Internal Security Operations Command (ISOC), a military unit dealing with national security, recently told local media it would continue to prevent refugees from entering Thailand. The ISOC did not reply to a request for comment.

In an open letter this week, campaign group Fortify Rights urged Thailand to abandon its “push back” policy.

“Thailand’s leaders should be doing all they can to stem the violence in Myanmar and prepare to provide protection to refugees fleeing the attacks,” executive director Amy Smith said.

Thailand does not recognise the status of any refugees or recognise the Rohingya as legitimate migrant workers.